Deposition and etching in a plasma environment are two of the most common steps used to form patterned layers in integrated circuit manufacturing. Controls on chemical composition and impurity levels within the process chamber are crucial to the success of these steps. To ensure that a correct quantity of film is deposited or etched, the plasma state in the process chamber needs to be monitored during a plasma process. Optical emission spectrometer (OES) is a commercially available device which is used to detect the presence and relative concentrations of various gas species in a process chamber. The optical emission spectrometer works by measuring emission intensity of the species in the plasma as a function of wavelength. The OES readings are statistically analyzed to identify gaseous species and relative concentration levels of identified gases within the process chamber. The OES readings may be used to determine a processing end-point.
However, the existing OES only provides intensity measurement of the species throughout the radial distance of the plasma. The existing OES is unable to monitor emission intensity of the species at specific locations of the plasma. Therefore, there is a need in the art to provide an improved plasma monitoring device that can provide emission intensity of the species at specific locations of the plasma.